(a) Field of the Invention
The present invention relates to a display device and a driving method thereof, and in particular, to a liquid crystal display.
(b) Description of Related Art
Generally, a liquid crystal display (LCD) includes a pair of panels including a plurality of pixel electrodes and a common electrode and a liquid crystal (LC) layer interposed between the panels and having dielectric anisotropy. The pixel electrodes are arranged in a matrix and connected to switching elements such as thin film transistors (TFTs). The pixel electrodes are supplied with data voltages through the TFTs row by row. The common electrode ranges over an entire surface of a panel and is supplied with a common electrode. The pixel electrode and the common electrode along with the LC layer disposed therebetween form LC capacitors in circuital view, and a LC capacitor as well as a switching element is a basic element forming a pixel.
The LCD generates electric field in the LC layer by applying voltages to the electrodes, and obtains desired images by controlling the strength of the electric field to varying the transmittance of light incident on the LC layer.
Among the LCDs, a vertical alignment (VA) mode LCD, which aligns LC molecules such that the long axes of the LC molecules are perpendicular to the panels in absence of electric field, is spotlighted because of its high contrast ratio and wide reference viewing angle.
The wide viewing angle of the VA mode LCD can be realized by cutouts in the field-generating electrodes and protrusions on the field-generating electrodes. Since the cutouts and the protrusions can determine the tilt directions of the LC molecules, the tilt directions can be distributed into several directions by using the cutouts and the protrusions such that the reference viewing angle is widened.
However, the VA mode LCD has poor lateral visibility as compared with front visibility. For example, a lateral gamma curve is different from a front gamma curve.
To improve the lateral visibility, a pixel is divided into two subpixels capacitively coupled to each other. One of the two subpixels is directly supplied with a voltage, while the other is subjected to voltage drop by the capacitive coupling such that the two subpixels have different voltages to cause different transmittances.
However, the conventional method may not control the transmittances of the two subpixels. In particular, since the transmittance is varied depending on the color of light, it is preferred that the voltages for different colors are different, but it may not be possible. Furthermore, the aperture ratio is reduced due to the addition of conductors for capacitive coupling, and the transmittance is reduced due to the voltage drop caused by the capacitive coupling.
In the meantime, the polarity of the data voltages relative to a common voltage is inverted every frame, every predetermined number of row or columns, or every pixel for preventing disadvantages including degradation caused by a long-time application of a unidirectional electric field. Among the inversion schemes of the data voltages, a column inversion, which reverses the polarity of the data lines every predetermined number of pixel columns, keeps the polarity of the data voltages applied to a data line for a predetermined time to reduce the signal delay of the data lines and to reduce the power consumption.
However, the column inversion may cause vertical flickering and vertical crosstalk to degrade the image quality of the LCD.